1. Field of Invention
The present invention relates to digital video frame buffer compression, and, more specifically to an efficient referencing frame image compression method that results in the saving of memory density, the time of accessing the referencing image and reduction of power consumption.
2. Description of Related Art
ISO and ITU have separately or jointly developed and defined some digital video compression standards including MPEG-1, MPEG-2, MPEG-4, MPEG-7, H.261, H.263 and H.264. The success of development of the video compression standards fuels wide applications which include video telephony, surveillance system, DVD, and digital TV. The advantage of digital image and video compression techniques significantly saves the storage space and transmission time without sacrificing much of the image quality.
Most ISO and ITU motion video compression standards adopt Y, Cb and Cr as the pixel components, which are derived from the original R (Red), G (Green), and B (Blue) color components. The Y stands for the degree of “Luminance”, while the Cb and Cr represent the color difference been separated from the “Luminance”. In both still and motion picture compression algorithms, the 8×8 pixels “Block” based Y, Cb and Cr goes through the similar compression procedure individually.
There are essentially three types of picture encoding in the MPEG video compression standard. I-frame, the “Intra-coded” picture uses the block of 8×8 pixels within the frame to code itself. P-frame, the “Predictive” frame uses previous I-type or P-type frame as a reference to code the difference. B-frame, the “Bi-directional” interpolated frame uses previous I-frame or P-frame as well as the next I-frame or P-frame as references to code the pixel information. In principle, in the I-frame encoding, all “Block” with 8×8 pixels go through the same compression procedure that is similar to JPEG, the still image compression algorithm including the DCT, quantization and a VLC, the variable length encoding. While, the P-frame and B-frame have to code the difference between a target frame and the reference frames.
In decompressing the P-type or B-type of video frame or block of pixels, accessing the referencing memory requires a lot of time. Due to I/O data pad limitation of most semiconductor memories, accessing the memory and transferring the pixels stored in the memory becomes bottleneck of most implementations. One prior method overcoming the I/O bandwidth problem is to use multiple chips of memory to store the referencing frame which cost linearly goes higher with the amount of memory chip. Some times, higher speed clock rate of data transfer solves the bottleneck of the I/O bandwidth at the cost of higher since the memory with higher accessing speed charges more.
The method and apparatus of this invention significantly speeds up the procedure of reconstructing the digital video frames of pixels without costing more memory chips or increasing the clock rate for accessing the memory chip.